1. Field of the Invention
The invention relates to a brake hose formed by the lamination of a plurality of rubber layers and reinforcing layer, which is used in automobiles and the like.
2. Description of the Related Art
A conventional brake hose used in automobiles is described in JP-A-63-303,288 or JP-A-6-305,083 (see FIG. 11). FIG. 11 is a cross section of the main components of a conventional brake hose 100. The brake hose 100 is formed by laminating several layers of rubber and yarn layers because of the need for high pressure resistance against brake hydraulics. That is, the brake hose 100 is formed by laminating an inner tube rubber layer 102 forming a flow path 101 for flowing brake oil, a lower yarn layer 104, an intermediate layer 106, an upper yarn layer 108, and an outer tube rubber layer 110.
The brake hoses 100 are used for long periods of time in an environment involving elevated temperatures and high humidity. In such environments, moisture from the atmosphere can sometimes penetrate through the outer tube rubber layer 110 into the interior layers and become dissolved in the brake fluid, causing vapor locks and compromising the pedal feel. Known techniques to overcome this drawback include the use of IIR with better water penetration resistance in the intermediate rubber layer (JP-A-63-303) and the use of EPDM/IIR two-layer rubber for the inner tube rubber layer (JP-A-6-305,083). Both of these conventional techniques result in better, although still not satisfactory, resistance to water penetration, and not only odes the latter technique require double-layer extruders, but the control of the thickness of the inner tube rubber layer is complicated.